This invention relates to a hammer-activated powder-actuated fastening tool. Powder-actuated fastening tools are used for driving fasteners or studs into concrete and other material. Such tools are conventionally of two types -- high velocity and low velocity. A low velocity tool includes a piston which is driven by the explosive force of a fired cartridge and drives the fastener into the workpiece, i.e., the material into which the fastener is driven. A high velocity tool does not include a piston, and the fastener is driven directly by the explosive force of the cartridge.
Several low velocity stud drivers are available. One type of low velocity tool is described in U.S. Pat. No. 3,066,302 and includes a means for resetting the piston to its firing position at the rear or breech end of the piston guide. This tool is a pistol-type tool which uses a trigger and sear to trip a spring-loaded firing pin. The firing pin is cocked by pushing the muzzle end of the tool against the workpiece to move the piston guide rearwardly within the tool housing and to compress the spring.
Pistol-type low velocity stud drivers are quite popular, but they are relatively expensive. For this reason hammer-activated stud drivers have been offered. Hammer-activated stud drivers are conventionally operated by placing the muzzle end of the tool against the workpiece and striking the rear end of the tool with a hammer to fire the cartridge. Such tools do not need the trigger and sear mechanisms and are less expensive than the pistol-type stud drivers. However, the relative simplicity of the hammer-activated tools provides certain disadvantages. For example, the tool may be inadvertently drop-fired, i.e., the cartridge may be fired if the tool is accidentally dropped on its rear end. Also, it is generally more difficult to load and unload hammer-activated tools than pistol-type tools. One type of hammer-activated tool is described in co-owned U.S. Pat. No. 2,768,375, but this tool is a high velocity tool. To the best of our knowledge, there is only one low velocity hammer-driven powder-actuated stud driver on the market.